[unreadable] Numerous conditions in the neonate result in cholestasis, or impairment of bile flow. Understanding biliary development is key to understanding the mechanisms by which many of these diseases are caused, yet fairly little is known regarding biliary development at a molecular level. The zebrafish model has emerged as an excellent model to study development in general, and appears to share several features with mammals with respect to biliary development. We propose studies in which we can identify and characterize genetic pathways that regulate aspects of biliary development in the zebrafish. In the first specific aim, we expand our studies of hnf-6 in zebrafish biliary development. The transcription factor hnf-6 has been shown to be important in the remodeling of bile ducts during liver development in the mouse; we have found a similar role for hnf-6 in zebrafish. We propose a closer examination of the timing of hnf-6 expression during development. The second specific aim involves mapping and identification of the gene responsible for mda, a biliary development mutant identified in a mutagenesis screen utilizing a unique lipid reporter, PED-6. PED-6, a quenched fluorescent lipid, is swallowed by larval zebrafish, becomes unquenched in the intestine, and is eventually taken up by the liver and excreted into the bile, concentrating in the gallbladder. In the third aim, PED-6 will be used in ongoing efforts in this mutagenesis screen, looking for mutants that fail to concentrate PED-6 in the gallbladder, suggesting a possible defect in the anatomy of the bile ducts. [unreadable] The information that can be obtained through the studies outlined in this proposal should provide insight into molecular aspects of zebrafish biliary development. These studies in zebrafish may provide clues as to biliary development in mammals and to genetic contributions to cholestatic diseases in humans [unreadable] [unreadable]